1. Field of the Invention
The present invention relates to a press for use in a lateral sealing process in a high-speed filling and packaging apparatus for manufacturing package containers each having a rectangular shape in cross section and filled with a fluid such as juice, particularly to a press provided with a hydraulic cylinder.
2. Prior Art
There is known a conventional filling and packaging apparatus comprising a rewinder for supporting a web serving as a packaging material (hereinafter referred to simply as packaging material web) in a rolled state, a winding apparatus for winding the web in order from the rewinder, a tube-forming apparatus for forming the wound web in a tubular shape after sterilizing it, a fluid supply pipe for filling fluid in the packaging material web which was formed in the tubular shape, and a container-forming apparatus for laterally sealing the web and cutting sealed parts of the web to continuously form pillow-like containers each having a rectangular shape in cross section while downwardly supplying the tube filled with the fluid by the length corresponding to one container, and a container shaping apparatus for bending each end part of the pillow-like containers which are separated into individual ones to shape each pillow-like container in a parallelepiped container to be finally obtained (as disclosed in JP-B 1-23366 and JP-A 58-193206)).
The aforementioned container-forming apparatus nips a tube filled with a fluid content by a length corresponding to one container and seals it laterally, and cuts the intermediate portion of the sealed part of the tube as disclosed in JP-B 1-23366, wherein it comprises two pairs of seal bars respectively disposed to oppose each other and a press for producing a sealing pressure between a pair of seal bars when they are positioned in a closing position where they approach each other.
The above-mentioned conventional press comprises a stationary engaging member which is disposed at both right and left sides of one of the paired seal bars and has an upward engaging recess and a movable engaging member which is disposed at both sides of the other of the paired seal bars and has a downward engaging protrusion engaging with the engaging recess of the stationary engaging member. The movable engaging member is secured to a piston rod of a hydraulic cylinder, and the piston rod is retreated in a state where the movable engaging member moves pivotally to engage with the stationary engaging member so that a sufficient sealing pressure of about 700 Kgf is produced between the seal bars.
The production of sealing pressure in the press owing to the retreat of the piston rod which is secured to the movable engaging member is performed by the oil under pressure of the hydraulic cylinder provided in the press, while the release of the sealing pressure and the advance of the piston rod is performed by the resilient force (about 30 Kgf) of a plurality of springs which are disposed coaxially in the cylinder and have different diameters at the same time when the hydraulic pressure is released, (e.g., see FIG. 12 of JP-B 1-23366). An idea to employ a biasing force other than the resilient force of the spring as a means for advancing the piston rod to which the movable engaging member is secured has not been hitherto considered in view of a space and cost of the lateral sealing apparatus having such a complex construction, and a need for such sealing apparatus has not been demanded so far. The springs provided in the hydraulic cylinder show durability as designed, and is sufficient to be replaced with another once a couple of months.
The inventors of the application have developed a superhigh-speed filling and packaging apparatus capable of manufacturing containers at a rate far in excess of 6000 pieces per hour which has been made so far, namely, more than 8000 pieces of containers per hour (as disclosed in Japanese Patent Application No. 8-244707). If the lateral sealing is performed at high speed using a conventional press in such a high-speed filling and packaging apparatus, it is newly found that since the hydraulic cylinder having springs therein is movable pivotally at higher speed than the conventional filling and packaging apparatus, there occur various problems such as breakage of springs for a short period of time and breakage of the engaging members at the portion where they engage with each other, which have not been considered in the press of the conventional filling and packaging apparatus.
When either of the springs provided inside the hydraulic cylinder, which is positioned at the back of the movable engaging member provided at both right and left sides of the seal bars, are broken, a piston rod which is retreated by hydraulic pressure in the hydraulic cylinder and to which the movable engaging member to which the sealing pressure is applied is not advanced although the sealing pressure is lost since the biasing force or the resiliency of the springs does not operate even if hydraulic pressure is not applied. In this case, since the sealing pressure is not applied to the movable and stationary sealing members which engage with each other, the movable and stationary sealing members disengage from each other owing to the upward pivotal motion of the piston rod. However, when the piston rod is moved downward pivotally for engaging the movable and stationary sealing members, the tip ends of the movable and stationary sealing members do not engage with each other once in several times depending on the situation, leading to a problem that the sealing pressure is not applied to the movable and stationary sealing members.
As a result, the press does not normally operate so that a package container in which incomplete lateral sealing is performed is manufactured, which causes a problem that a filler such as juice is leaked from the package container. If such leakage of the filler such as juice from the package container is visually recognized, it can be checked in a manufacturing process, but if such leakage is not visually recognized, it is very troublesome.
The reason is that in distribution channels of the germ-free filling and package container, such leakage of juice from the sealed parts causes a serious problem of propagation of the fungicide, etc. and contamination by a microorganism.
Since the springs are provided in the hydraulic cylinder, the damaging state of the springs cannot be seen from the outside. Even if either spring is damaged or broken during the manufacturing of the package container, the manufacture of the package container continues while either spring is damaged or broken, and hence there occurs a case that the damage or breakage of either spring is found out when the apparatus is checked upon completion of a day's manufacture so that all package containers manufactured at the same date must be scrapped. To avoid such a situation in advance, it is necessary to regularly replace either spring with another within a short period of time of about at least once a week anticipating safety, which incurs a troublesome labor to regularly replace either spring and also the increase of running cost involved in the replacement of either spring.